Prior art methods of truss construction used in large space structures include at least two basic methods: (1) construction of an erectable truss structure with individual components interconnected on orbit, and (2) deployable truss structures which expand from a stowed position to an expanded or deployed position on orbit.
One previously proposed method for assembling an erectable truss structure in space according to the first method listed above utilizes an assembly work platform, a mobile transporter, and an astronaut positioning system. Crew members connect struts, in space, which are 5 meters long and 2 inches in diameter to build the necessary truss structure. After assembling the truss structure, the crew members attach all the space station utilities and subsystems to the truss. After all connections of the subsystems are complete, the integrated subsystems are checked out and verified on-orbit.
According to this proposed method, a mobile transporter translates assembled truss sections out of the work area, which typically would be the payload bay in a shuttle spacecraft such as the space shuttle orbiter. The mobile transporter would also transport robotic arms and other hardware along the face of the truss. The mobile transporter moves with an "inch worm" type motion whereby part of the mobile transporter first moves forward on the truss and secures itself. Then the second half of the mobile transporter releases itself and pulls up to the first half. This truss structure includes a separate rail structure for translation of crew members along the truss structure. The astronaut positioning apparatus would typically include a robotic arm attached to the truss structure which would position an astronaut at various places along the truss structure for construction/repair purposes.
The above described construction method has a number of problems. Due to the large amount of extra vehicular (outside the space shuttle orbiter) activity required, it is difficult, hazardous, and time consuming to build the erectable truss. Since there are so many assembly operations in orbit, there is a high risk that interface problems or other malfunctions would occur. These problems could result in the loss of the space station or loss of a shuttle mission. The operation and construction of the "inch worm" mobile transporter is also complex, and the device would likely be subject to numerous electrical and mechanical problems. The additional rail for translation of crew members must also be assembled onto the truss, and is quite heavy.
Due to the large amount of on-orbit assembly, the above construction method for erecting a truss structure requires a significant amount of flight support equipment. One necessary element of flight support equipment is an assembly work platform, which is relatively complicated and requires on-orbit assembly. The mobile transporter needs to be attached to the assembly work platform to provide capability to translate the truss out of the payload bay as it is assembled.
Also, according to this same proposed method, another necessary flight support element is an astronaut positioning system. This system is comprised of two robotic arms for positioning two astronauts as necessary to assemble the truss and affix hardware to the truss. The astronaut positioning system is complicated, expensive, and heavy.
A utility spool is yet another flight support element of this proposed system. The spool includes utilities such as power, data, video, cooling fluids, waste gas fluids, etc. During the truss assembly, the utility lines are wound off the spool onto the truss. The spool is a large, heavy piece of flight support equipment and is required to erect the truss using this construction method. According to this proposed prior art construction technique, the failure of either the assembly work platform, mobile transporter, spool, or astronaut positioning system could cause loss of a mission success and possibly loss of the space station.
The alternative deployable truss, once launched into space, typically extends linearly from a stowed position to a deployed position while on orbit. Crew members then attach all the space station utilities and subsystems onto the structure after it had been deployed. This design also uses the "inch worm" type mobile transporter.
A problem with the deployable truss is that it cannot be assembled with the sub-systems attached to it for checkout on the ground. This is because the structure is not designed to withstand the one g loading environment which occurs on Earth. The deployable truss is thus not complete upon deployment. Subsystems such as power, data, and plumbing, still have to be added on-orbit after deployment. A rail must be added for crew and equipment translation. An additional risk of the deployable truss is that the deployment may not be complete or may be prevented due to a malfunction of one of the very many deployment mechanisms.
Due to its relatively light construction, the deployable truss is also susceptible to damage from micro-meteoroids, orbital debris, and crew induced loading. For this reason, thorough periodic inspections are required on-orbit for this structure. If defects are detected, it is necessary to have the capability to repair or replace damaged components.
U.S. Pat. No. 4,587,777 to Vasques, et al. discloses a deployable space truss. The truss is transported in a collapsed position and extended once in place. It is anchored to an orbiting hub prior to further assembly or the inclusion of utility subsystems. The deployable truss does not have a mobile transporter capable of translating the truss to a position where more truss segments can be added.
U.S. Pat. No. 4,978,564 to Douglas discloses a space station structural element which has embedded electrical lines and which is flexible in nature. It includes a self-deploying structural element having a core of temperature sensitive expanding foam, a load carrying outer component of advanced composite material, and an outer retaining jacket. The heating of the structure causes the foam to cure and expand for deployment. This invention is not a truss with integrated utilities.
U.S. Pat. No. 4,807,834 to M. Cohen discloses an integration channel for subsystems in a space station. The berthing components allow electrical connections to existing modules. The application is directed towards pressurized modules and their interconnections, rather than truss segments pre-integrated to include utility subsystems.
U.S. Pat. No. 4,872,625 to C. Filley discloses a universal module assembly including a pressure vessel having cylindrical side walls and curved end surfaces. A rigid external supporting framework is attached to the exterior of and surrounds the pressure vessel. The main body portion has the general configuration of a right hexagonal prism, and the end portions of the framework are generally frustoconical. The universal modules do not include open truss structures. The universal module is pressurized and does not allow for deployable subsystems such as solar panels and radiators.
Consequently, a need exists for improvements in apparatus and method for constructing a space station to decrease the high costs, as well as the complexity and difficulties of on-orbit assembly. Those skilled in the art have long sought and will appreciate the novel features of the present invention which solve these problems.